This disclosure relates generally to proximity detection systems at work sites, and in particular to an interactive magnetic marker field and proximity detection system. Mining is a very diverse industry, in many ways. The diversities include the differing product being mined, geologic formations from which the product is being extracted, locations throughout the world, strategies for mining, countless types of equipment used, mining above ground and underground, to mention a few examples. In most cases, equipment is being used to accomplish or to assist in the mining process including mining machines and vehicles. Such vehicles and mobile equipment may be used for above and/or below ground operations. Examples of the equipment include: road construction equipment such as trucks, road graders, rollers and pavers; surface mining equipment, such as for use with gravel and sand operations, front end loaders, trucks, dozers, conveyors and other items; underground mining equipment such as continuous miners, shuttle cars, conveyors, crushers, load-haul-dump vehicles, man-trips, tractors, and other items. The equipment also includes non-mining equipment, for example forklifts, cranes, and trucks used at warehouses and shipping ports.
Much too often, workers are injured while doing their jobs. As more equipment is used and as that equipment has become larger and more powerful. And as the operations have become more complex, many of the injuries and fatalities result from workers being struck or crushed by the mining machines or by collisions between vehicles.
Many methods have been devised to warn people against being struck, pinched, crushed or otherwise harmed by vehicles and mobile equipment. Unfortunately, the systems that have been devised to help protect people and property in these industrial operations, such as proximity detection and collision avoidance systems, have usually not been very effective. A new proximity detection system was developed and successfully demonstrated for use on continuous miners, as disclosed in U.S. Pat. No. 7,420,471 (the '471 patent), U.S. Pat. No. 8,169,335 (the '335 patent) and U.S. Pat. No. 8,232,888 (the '888 patent), and US patent publications 2009/0322512 (the '512 publication) and 2010/0271214 (the '214 publication), which patents and publications are herein referred to collectively as the “Frederick patents,” the disclosures of which are incorporated herein by reference in their entireties. An objective of the '471 patent is to help prevent the crushing or pinning of personnel who are remotely controlling a continuous miner, and to help protect other personnel assisting in use of the continuous miners. The '471 patent also envisions to provide protection to personnel from other types of mobile equipment and machines. The system of the '471 patent employs a magnetic marker field and an active architecture that incorporates two-way communication between the worker and the machine the worker is near. Warnings are given to workers that are too close to the miner. Warnings are also provided to the operator of the machine. Provisions are made to immobilize the equipment until personnel are able to reach a safer position.
The magnetic fields used in the '471 patent system oscillate at low frequencies and can be effectively used to mark off warning zones, danger zones and silent zones. Although the maximum practical range of such low frequency (LF) magnetic fields may be as much as one hundred feet, in most applications that is more than is needed or desirable for most equipment. Typical very large off-highway haul trucks would probably be best served with a warning zone in the range of eighty feet and a danger zone in the range of thirty to forty feet. In some applications, such as remotely controlled continuous miners, it is necessary for the operator to remain within a range of five to ten feet much of the time in order to maintain good visual contact with the machine and the immediate surroundings. The zones are shaped to be longer in the direction of travel or movement but less in directions perpendicular to the direction of travel. In underground mines, the low frequency magnetic fields pass through earth formations unimpeded so that a worker that is around a corner, not in line of sight, or otherwise obstructed, will still be visible to the marker field. These magnetic fields do not radiate from antennas but simply expand and contract around the element that produces them, and are well suited for marking boundaries between silent zones and warning zones.
Proximity detection systems are beginning to be deployed in many types of mining operations around the world in an effort to avert mining accidents related to the use of machines and vehicles. As this technology advances, there is an increased need for higher performance from these systems.
Experience has confirmed that the most effective proximity detection systems utilize low frequency magnetic fields to establish markers or zones in which workers are sufficiently safely positioned with respect to a machine, and to establish separate zones that are not sufficiently safe. These systems are also effective for helping to avoid collisions between vehicles that are moving at slow speeds or are moving in a direction where visibility is limited. Statistics show that most accidents, including most fatalities, occur when the vehicles are moving at slow speed, have just started to move after having been stopped, or are moving in reverse. In some work site situations, multiple vehicles and machines might operating closely together and many personnel might be in close proximity to one or more of these machines or vehicles. The congested conditions increase the likelihood of accidents. Thus it is particularly desirable that the elements of proximity detection systems, whether located on the machines and/or vehicles or on the personnel, work properly in these congested conditions to provide the protection that is needed. Moreover, experience has shown that it is highly desirable that the systems not give false alarms because that gives rise to loss in confidence in the systems and leads to the systems not being used, not only when in congested areas, but at other times as well. The systems must be reliable at all times.
An example of a typical situation in an underground coal mine where congestion is experienced would be when shuttle cars are being loaded by a continuous miner or are waiting their turn to be loaded. A continuous miner will typically be sumping into the coal formation or its cutter will be shearing down into the coal, while a shuttle car is following and is being loaded. Occasionally, a first shuttle car does not get loaded in the usual amount of time so that other shuttle cars return from dumping their loads before the first car has been loaded. As a result, the first shuttle car is still being loaded while the others, typically two, are nearby, awaiting their turns. All three shuttle cars will be equipped with proximity systems, as well as the continuous miner, while there can also be one or more special proximity modules near that same location that provide protection from other dangers. Each of these machines will typically have an operator and there are often other mining personnel assisting the operation in some way and/or are observing or inspecting the operation. This is only one example of an almost endless range of possible situations where multiple proximity systems must work reliably at all times. It is in such situations where extra demands are placed upon the proximity systems to be able to protect all workers from all machines and vehicles without conflicting or confusing the personnel or impacting the proper operation of the equipment.
Currently, the proximity systems that are based on the preferred low frequency magnetic fields have limitations that will become significant with increasing demands upon the systems. Consider the situation described above where there are multiple machines positioned near each other and there are multiple workers around the machines. In this operational configuration, the safety zones for the multiple machines overlap. Personal alarm devices (PADs) being carried by workers, must reliably respond to each safety zone so that they are protected from being hit or crushed by any machine. The magnetic fields produced by the systems must not conflict or interact and produce zone shapes other than those intended. The magnitude of the challenge is easily seen when the number of generators is considered. In the example where there are three shuttle cars and one continuous miner, each having four generators, and each generator having to operate independently of other generators in order to produce shaped fields, there are a total of sixteen generators operating within the environment. If each is required to produce a zone four times per second then there must be fields produced sixty-four times per second. Although the generators on a machine can be coordinated by the central controller on that machine so as to not conflict with each other, the generators on the other machines will produce fields according to their own timing and might conflict (e.g., by producing their respective magnetic fields in a common area at the same time so that a PAD in the common area would experience a field strength resulting from the addition of the two fields). Currently, this challenge is being met by a variety of workarounds and techniques. Moreover, there are situations in surface mining in which many vehicles may be congregated in a small area and the zone sizes are much larger. The challenges of avoiding conflicts are growing as the technology is being advanced and utilized in more crowded work sites. Therefore, there is a need for a system and method to decrease the likelihood of conflicts between proximity detection systems.